A known valve timing control apparatus, disclosed in JP3191865B, includes a housing member and vane members. The vane members are respectively accommodated within hydraulic pressure chambers, formed at radially inner side of a circumferential wall of the housing member, so as to be rotatable relative to the housing member within a predetermined angle range. The housing member is configured by a front-side wall, the circumferential wall and a rear-side wall. The circumferential wall includes shoes for forming the hydraulic pressure chambers. The front-side wall and the circumferential wall are integrally formed by aluminum die-casting. The rear-side wall is formed separately from the front-side wall and the circumferential wall. The rear-side wall includes a timing gear.
According to the valve timing control apparatus, disclosed in JP3191865B, the circumferential wall and the front-side wall of the housing are integrally formed. Therefore, seal members for sealing connecting points of the circumferential wall and the front side wall may not be necessary. In a case where the seal members are not provided, an outer diameter of the housing member may be shortened. Further, the circumferential wall and the front-side wall of the housing are integrally formed. Therefore, a coaxial alignment of the circumferential wall and the front-side wall may not be necessary.
The rear-side wall of JP3191865B includes a timing gear for transmitting a driving force. Therefore, the rear-side wall is generally made of high-quality metal material, having abrasion resistance and sufficient strength. Further, the rear-side wall needs to be formed in a manner where a dimension thereof is sufficiently large so that a rear opening portion of the circumferential wall is closed by the rear-side wall in order to form the hydraulic pressure chambers. Therefore, because of the existence of the rear-side wall, the valve timing control as a whole may become expensive and a weight thereof may be increased.
A need thus exists for a valve timing control apparatus which is not susceptible to the drawback mentioned above.